Funds are requested to purchase a Philips CM 12 Scanning Transmission Electron Microscope equipped with eucentric goniometer, cold stage, and x-ray spectrometer. Provided will be a microscope of contemporary design to be used as the major research instrument in a multiuser facility shared by six PHS grantees as well as other biological scientists from three departments (zoology, botany-microbiology, and chemistry). It will replace older, inadequate instrumentation and allow us to proceed with PHS-funded research in the following areas: a) maturation and early development in mammalian oocytes, b) localization of mRNA and cytoskeletal proteins during maturation of Xenopus eggs, c) redistribution of cell calcium during exocytosis in secretory cells, d) extracellular coats on sea urchin and amphibian eggs and ultrastructural modifications of these during fertilization, e) immunocytochemical localization of snake venom myotoxins, and f) binding and mode of action of bacterial mosquito-larvicidal toxins.